Cathode ray tube with light-modulated fluid filling space between rotatable disc and output window



May 28, 1968 H. E TOWLSON 3,385,991l

CATHODE RAY TUBE WI'IH LIGHT-MODULATED FLUID FILLING SPACE BETWEEN ROTATABLE DISC AND OUTPUT WINDOW Filed Feb. 5, 1965 INVENTOR HOWARD E. TOWLSON,

ms ATTORNEY.

United States Patent 3,385,991 CATHODE RAY TUBE WITH LiGHT-MGDULATED FLUID FILLING SPACE BETWEEN ROTATABLE DISC AND OUTPUT WINDOW Howard E. Towlson, Baldwinsville, N.Y., assignor to General Electric Company, a corporation of New York Filed Feb. 5, 1965, Ser. No. 430,700 6 Claims. (Cl. 313--91) The present invention relates to a light valve apparatus and, more specifically, to a light valve tube suitable for the projection of a television image.

One form of light valve tube suitable for the projection of a television image comprises an evacuated envelope in which is positioned an electron gun in alignment with a transparent disc, the disc being rotatable through a reservoir of light modulating fluid to deposit a continuously replenished layer of light modulating fluid thereon. An electron beam generated by the electron gun is directed through electrostatic beam deflecting and focusing means and is scanned across a portion of the light modulating fluid layer, the beam being controlled to selectively deform the fluid layer. The fluid deformations thus formed constitute diffraction gratings which,

in conjunction with a light source and a Schlieren optical system, serve to selectively control the passage of light from the source through the rotatable disc to an output window in the tube envelope.

Several problems are encountered in the operation of such a light valve tube. Initially, the light modulating fluid tends to condense on the output window or to form droplets thereon, thereby resulting in non-uniform optical properties which severely interfere with the projection of a satisfactory image. Somewhat similarly, since the rotatable disc is necessarily rotated through a reservoir of light modulating fluid a fluid layer is formed on the output surface of the disc adjacent the output window, this layer being non-uniform because of gravitational effects and thus impairing the operation of the tube unless smoothed or removed. Further, internal light reflections between the output surface of the rotatable disc and the output window severely reduce the contrast ratio obtainable for a projected image. Even further,- slight-imperfections on the surfaces of the rotatable disc and output window such as minute scratches cause light scattering which further decreases the obtainable contrast ratio.

The present invention eliminates the above described problems in a simple and reliable manner to thereby provide improved light valve tube operation.

Accordingly, an object of the invention is to provide an improved light valve tube suitable for the projection of a television image.

Another object is to provide an improved light valve tube wherein the region between the rotatable disc and output window exhibits uniform optical properties.

Another object is to provide an improved light valve tube wherein adverse effects produced by a non-uniform fluid coating on the output surface of the rotatable disc and by fluid condensate or droplets on the output window are eliminated.

Still another object is to provide a light valve tube whereby an improved contrast ratio is obtained by minimizing adverse effects due to internal light reflections and surface irregularities.

These and other objects are achieved in one embodi' ment of the invention through the use of a generally planar output window which extends into the reservoir of light modulating fluid and which is spaced from the rotatable disc by a distance such that capillary action causes the light modulating fluid to fill the region be- 3,385,991 Patented May 28, 1968 ice tween the rotable disc and the output window. In this manner the region between the rotatable disc and the output window exhibits uniform optical properties and problems due to reflection and scattering are minimized.

In a preferred embodiment of the invention, the small spacing necessary to achieve the desired capillary rise is achieved through the use of protuberances positioned on the output window and ground to the desired capillary spacing, the rotatable disc being positioned in abutment with the protuberances and thus in the desired spaced relationship with the output window.

The novel and distinctive features of the invention are set forth in the appended claims. The invention, itself together with further objects and advantages thereof, may best be understood by reference to the following description and accompanying drawings in which:

FIGURE 1 is a simplified cross-sectional view of the light valve tube of the invention.

FIGURE 2 is a front view partially broken away of the tube of FIGURE 1, and

FIGURE 3 is a preferred embodiment of the output window as employed in the light valve tube of FIG- URE 1.

Referring to FIGURE 1 there is shown a light valve tube 1 in accordance with the invention for positioning between a light source and a screen (not shown) for the projection of a television image to the screen.

The light valve tube 1 comprises an evacuated envelope 2 in which is positioned a rotatable transparent disc 3 having a transparent conductive coating 4 positioned on one surface thereof.

The rotatable disc 3 is provided with a centrally located bearing 5, the bearing 5 receiving a shaft 6 and allowing the rotation of the disc 3 in its own plane about its center through a reservoir 7 of light modulating fluid.

The shaft 6 is supported by a generally planar shield 8 having a centrally located aperture: 9 therein, the shield 8 being attached to the envelope 2 by any suitable means (not shown).

The rotatable disc is rotated by a drive means 10 positioned within a protuberance 11 in the envelope 2, the drive means 10 including a shaft 12 having a drive member 12 operably engaging the periphery of the rotatable disc 3 as shown more clearly in FIGURE 2.

Rotation of the disc 3 through the reservoir 7 causes a continuously replenished layer of light modulating fluid 13 to form on the conductive coating 4.

An electron gun 14 is positioned in a necked-down portion 15 of the envelope 2. The electron gun 14 comprises an electron emitting cathode electrode 16 in conjunction with an electron lens comprising first electrode 17 and second electrode 13. The electron gun 14 generates an electron beam 19 which passes through the aperture 9 in the shield 8 to impinge upon the layer of light modulating fluid 13 to deposit charges thereon. The charges thus deposited are attracted to the conductive layer 4 to cause deformations 29 in the layer of light modulating fluid. The electron beam 19 is swept across the layer of modulating fluid 13 by electrosatic focus and deflection means (not shown), the beam being controlled to selectively deform the light modulating fluid to form a diffraction grating thereon.

In accordance with one embodiment of the invention, the envelope 2 is provided with a generally disc shaped output window 21, the output Window 21 extending into the reservoir of light modulating fluid 7. The output window 21 is spaced from the output surface of the rotatable disc 3 in generally parallel relationship thereto by a distance as defined by the dimension a such that the area between these members is filled with light modulating fluid 3 by capillary action. As depicted in FIGURE 3 the disc shaped output window 21 is provided with a slightly truncated portion 21' to prevent interference with the drive means 10.

In accordance with a preferred embodiment of the invention, the desired spacing between the output window 21 and rotatable disc 3 is achieved through the provision of a plurality of protuberances 22 on the output window 21 as shown more clearly in FIGURE 3.

The rotatable disc 3 is urged against the protuberances 22 by any suitable means such as the spring 23 surrounding the shaft 6, the disc 3 thus rotating in the desired spaced relationship with respect to the output window 21. The protuberances 22 are positioned so as to not interfere with the area of the rotatable disc 3 upon which the electron beam impinges.

The protuberances 22 might advantageously be formed from fritted glass droplets ground to provide the desired spacing between the output window 21 and rotatable disc 3.

In utilizing the light valve tube shown in FIGURE 1 for the projection of a television image, a light source (not shown) is positioned behind the electron gun 14. Light rays from the source are directed by a lenticular lens system 24 formed on the rear wall of the envelope 2 to the diffraction grating formed by the deformations 20. The lenticular lens system 24 is employed to increase the optical efiiciency of the system by dividing the light from the source into a number of discrete sources.

By modulation of the electron beam 19 through the application of suitable potentials to the electrostatic focus and deflection means, the direction grating formed by the deformations 20 in the layer of light modulating fluid 13 is selectively controlled. Thus, the light passing through the transparent rotatable disc 3 and the output window 21 is selectively controlled and in conjunction with externally located lenses of a Schlieren optical system projects an image representative of the electron beam modulating intelligence to a suitable screen.

In accordance with the invention, the problems of nonuniform optical properties in the region between the rotatable disc 3 and the output window 21 are prevented by spacing the rotatable disc 3 from the output window 21 by a capillary distance such that the region in question is filled with the light modulating fluid so as to present uniform optical properties.

It will be appreciated that since the rotatable disc 3 is rotated for example on the order of 3 revolutions per hour, the relative motion between disc 3 and the output window will tend to fill the area in question with light modulating fluid even in the absence of capillary action. However, if it is desirable that the area between the output window 21 and the rotating disc 3 be filled with light modulating fluid at all times even when the rotatable disc 3 is not rotating, then the capillary distance a must be such that capillary action alone will raise the light modulating fluid a distance defined by the dimension b to provide the necessary fill-in. On the other hand, if in some applications it is permissible that a time elapse between the starting of rotation of the disc and the achieving of the desired fill-in then the rotation of the rotatable disc 3 can be relied on to aid the capillary action in providing the necessary rise b. Thus, the term capillary distance as employed in this application relates to the dimension a necessary to achieve a desired rise 11 both in the situation when the disc 3 is rotating and the situation when the disc is not rotating.

The required spacing at for complete fill-in by capillary action when the rotatable disc 3 is not rotating can be computed from the following formula which applies to a pair of planar members having a spacing a much smaller than the width of the members as is the case in the light valve tube of the invention:

s(2 cos where:

b is the desired oil rise,

sis the surface tension of the fluid,

d is the density of the fluid,

g is the gravitational constant, and

0 is the acute angle at which the fluid meniscus intersects the output window or rotatable disc.

In a particularly successful embodiment of applicants invention wherein a light modulating fluid of the polybenzyl toluene type having a viscosity of 1000 centistokes and a density of 1.1 grams/cm. at an operating temperature of approximately C. was employed, a height b of 2.5 inches was achieved to provide complete fill-in during non-rotation of the rotatable disc 3 through the use of a dimension a of 0.003 inch.

Although the invention has been described with respect to certain specific embodiments, it will be appreciated that modifications and changes may be made by those skilled in the art without departing from the spirit and scope of the invention. Specifically, various other output window configurations might advantageously be employed.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A light valve apparatus for positioning between a light source and a screen for the projection of an image on the screen, said apparatus comprising:

(A) an evacuated envelope including a light transmitting output window therein,

(B) a reservoir of light modulating fluid positioned within said envelope,

(C) a rotatable disc positioned within said envelope in spaced relationship to said output window and arranged for rotation through said reservoir to produce a layer of light modulating fluid upon a surface of said disc,

(D) cathode means positioned in said envelope and arranged to emit a beam of electrons impingement upon said layer of light modulating fluid to form a diffraction grating thereon for selectively controlling the passage of light from the source through the output window to the screen in accordance with the image being projected, and

(E) means for conducting said light modulating fluid to the region between said output window and said rotatable disc to substantially fill said region with said light modulating fluid.

2. A light valve apparatus for positioning between a light source and a screen for the projection of an image on the screen, said apparatus comprising:

(A) an evacuated envelope including a light transmitting output window therein,

(B) a reservoir of light modulating fluid positioned within said envelope,

(C) a rotatable disc positioned within said envelope in spaced relationship to said output window and arranged for rotation through said reservoir to produce a layer of light modulating fluid upon said disc,

(D) cathode means positioned in said envelope and arranged to emit a beam of electrons impingement upon said layer of light modulating fluid to form a dilfraction grating thereon for selectively controlling the passage of light from the source through the output window to the screen in accordance with the image being projected, and

(B) said output window extending into said resewoir and being spaced from said rotatable disc by a capillary distance such that the region between said output window and rotatable disc is substantially filled by said light modulating fluid.

3. A light valve apparatus for positioning between a light source and a screen for the projection of an image on the screen, said apparatus comprising:

(A) an evacuated envelope including a generally planar light transmitting output window therein,

(B) a reservoir of light modulating fluid positioned within said envelope,

(C) a rotatable disc positioned within said envelope in generally parallel spaced relationship to said output window and arranged for rotation through said reservoir to produce a continuously replenished layer of light modulating fluid upon the surface of said disc most distant from said output window,

(D) cathode means positioned in said envelope and arranged to emit a beam of electrons impingment upon said layer of light modulating fluid to form a diffraction grating thereon for selectively controlling the passage of light from the source through the output window to the screen in accordance with the image being projected, and

(B) said output window including a depending portion extending into said reservoir and being spaced from said rotatable disc by a capillary distance such that the region between said output window and rotatable disc is substantially filled by said light modulating 4-. The apparatus defined in claim 3 wherein said output Window is generally disc shaped.

5. The apparatus defined in claim 3 wherein said output window is provided with a plurality of protuberances defining said capillary distance and said rotatable disc is rotated in abutment with said protuberances.

6. The apparatus defined in claim 5 wherein said protuberances are formed from fritted glass droplets ground to the desired capillary dimension.

No references cited.

ROBERT SEGAL, Primary Examiner. 

1. A LIGHT VALVE APPARATUS FOR POSITIONING BETWEEN A LIGHT SOURCE AND A SCREEN FOR THE PROJECTION OF AN IMAGE ON THE SCREEN, SAID APPARATUS COMPRISING: (A) AN EVACUATED ENVELOPE INCLUDING A LIGHT TRANSMITTING OUTPUT WINDOW THEREIN, (B) A RESERVOIR OF LIGHT MODULATING FLUID POSITIONED WITHIN SAID ENVELOPE, (C) A ROTATABLE DISC POSITIONED WITHIN SAID ENVELOPE IN SPACED RELATIONSHIP TO SAID OUTPUT WINDOW AND ARRANGED FOR ROTATION THROUGH SAID RESERVOIR TO PRODUCE A LAYER OF LIGHT MODULATING FLUID UPON A SURFACE OF SAID DISC, (D) CATHODE MEANS POSITIONED IN SAID ENVELOPE AND ARRANGED TO EMIT A BEAM OF ELECTRONS IMPINGEMENT UPON SAID LAYER OF LIGHT MODULATING FLUID TO FORM A DIFFRACTION GRATING THEREON FOR SELECTIVELY CONTROLLING THE PASSAGE OF LIGHT FROM THE SOURCE THROUGH THE OUTPUT WINDOW TO THE SCREEN IN ACCORDANCE WITH THE IMAGE BEING PROJECTED, AND (E) MEANS FOR CONDUCTING SAID LIGHT MODULATING FLUID TO THE REGION BETWEEN SAID OUTPUT WINDOW AND SAID ROTATABLE DISC TO SUBSTANTIALLY FILL SAID REGION WITH SAID LIGHT MODULATING FLUID. 